dissenting:
There is no dispute that Morgan has suffered from a mental impairment of disabling severity for a number of years; neither party challenges Morgan’s entitlement to Title XVI supplemental social security benefits due to psychosis attributed to paranoid schizophrenia. Rather, the central question presented by Morgan’s application for Title II disability benefits is whether the onset of Morgan’s disability occurred prior to the termination of his insured status on December 31, 1979.
The majority’s abbreviated treatment of Morgan’s mental disability claim dismisses two separate, yet related, evidentiary errors committed by the Secretary. Ignoring Social Security Ruling 83-20 (“SSR 83-20”) which establishes guidelines for determining the onset date of a claimant’s disability, as well as the more general administrative obligation to fully develop the record in social security cases, the Secretary erroneously concluded that no medical evidence supported an onset date prior to December 1979. The majority is able to affirm the Secretary only by flatly contradicting the plain language of SSR 83-20.
A.
SSR 83-20 provides specific evidentiary guidelines for ALJs when faced with an issue concerning the onset date of a disability. SSR 83-20 recognizes the necessity of inferring the date of onset in cases where either the nature of the disabling illness, or the lack of medical documentation bearing on the onset of disability in a particular case, precludes precise determination. When onset must be inferred, SSR 83-20 requires an AU to “call on the services of a medical advisor.” Finally, SSR 83-20 instructs exploration of other sources of documentation — such as family members, friends, and former employers — when reasonable inferences about the progression of the claimed impairment cannot be made from the case record and additional medical evidence is not available.
The relevant language from SSR 83-20 reads:
Precise Evidence Not Available— Need for Inferences
In some cases, it may be possible, based on the medical evidence to reasonably infer that the onset of a disabling impairment(s) occurred some time prior to the date of the first recorded medical examination, e.g., the date the claimant stopped working. How long the disease may be determined to have existed at a disabling level of severity depends on an informed judgment of the facts in the particular case. This judgment, however, must have a legitimate medical basis. At the hearing, the administrative law judge (AU) should call on the services of a medical advisor when onset must be inferred. If there is information in the file indicating that additional medical evidence concerning onset is available, such evidence should be secured before inferences are made.
If reasonable inferences about the progression of the impairment cannot be made on the basis of the evidence in file and additional relevant medical evidence is not available, it may be necessary to explore other sources of documentation. *1431Information may be obtained from family members, friends, and former employers to ascertain why medical evidence is not available for the pertinent period and to furnish additional evidence regarding the course of the individual’s condition.
Id., reprinted in 2 Social Security Claims: Practice and Procedure § 21.92 (Callaghan 1988).
This language is not complex, and is susceptible to only one reasonable interpretation. If there is a dispute about the onset of a disabling impairment, the ALJ’s judgment of how long a disease existed must have a legitimate medical basis. The legitimacy of the judgment depends on the AU calling on the services of a medical advisor, and on the AU receiving any other available medical evidence. The testimony of the medical advisor and all other available evidence must be heard “before inferences are made” about the onset date.
A straightforward reading of the cited passage of SSR 83-20 shows that the majority has misstated the Ruling when is asserts that “any inference of disability must have a legitimate medical basis.” What the Ruling says is that the AU’s judgment about whether such an inference can be made must have a legitimate medical basis. SSR 83-20 is a procedural safeguard to ensure that inferences are not made without the assistance of a medical advisor. The majority concludes from its misreading that “no medical advisor is necessary” when the AU decides — by what standard, the majority admits, it cannot explain — that no “medical basis can support an inference of disability.” But this is nonsense, for the whole purpose of SSR 83-20 is to require that a medical advisor be heard before the AU can be deemed to have a “legitimate medical basis” for a judgment based on inferences. The majority’s result not only stands SSR 83-20 on its head; it perpetrates a gross injustice on social security claimants, who would be denied SSR 83-20’s procedural protections for a fair determination of their claims, B.
Unlike broken bones or other physical ailments, mental illness does not generally appear overnight. Likewise, Morgan did not suddenly “become” schizophrenic in 1984. Onset and development of schizophrenia is typically insidious and variable, with behavioral or personality abnormalities presenting themselves slowly over time. See 1 Comprehensive Textbook of Psychiatry 758-59 (H. Kaplan & B. Sadock 5th ed. 1989) [hereinafter Textbook of Psychiatry ]; Diagnostic and Statistical Manual of Mental Disorders 190-91 (3d ed. rev. 1987) [hereinafter DSM-III-R j.1 Accordingly, any attempt to discern the onset of Morgan’s mental disability requires a broad longitudinal approach which traces the course of his mental condition from its alleged date of onset in 1977, through the period ending his insured status in December 1979, to the present. The majority’s abbreviated and narrowly-focused treatment of the evidence supporting Morgan’s claim for mental disability benefits thus paints an incomplete, if not inaccurate, portrait of his mental condition during the relevant time period.
A broad view of Morgan’s condition reveals a steady downward progression in his mental health commencing well before 1984. Morgan dates the onset of his mental difficulties to a hernia operation in late 1977. Shortly after release from the hospital, Morgan began to experience somatic symptoms including recurrent chest pains, rapid pulse, weakness, and exertional fatigue. He additionally complained of increasing anxiety and difficulty coping with daily life.2 During this period, Morgan *1432also received counseling from a community-mental health clinic in Crescent City, California.3
In the year following the expiration of his insured status in December 1979, Morgan sought treatment from numerous medical professionals who noted his deteriorating mental state. Only four weeks after his insured period ended, Morgan visited a hospital emergency room complaining of “extreme anxiety.” The attending physician noted Morgan’s state of distress in his report:
A 56 year old male who has been under a great amount of stress, including financial, job related and family for approximately the past 2 years. This has become progressively worse in the past year. He has been seen ... [by his treating physician] numerous times for tachycardia, chest pain; he has had several cardiac studies, including stress test. These have all been normal. The man now states that he has a potentially serious time in his life, he feels that he will explode if he can’t deal with the situation, claims that he is not a man.who comes to doctors, he feels he needs help....”
The physician encouraged Morgan to seek-counseling and prescribed a trial dose of Valium. In February 1980- — just six weeks after the expiration of his insured status— Dr. Dysart, a rheumatologist, described Morgan as “nearly incapacitated by severe depression and chronic anxiety with somati-zation.” Dr. Dysart prescribed medication and suggested that Morgan continue counseling at the Crescent City mental health clinic, but cautioned that “the severity of his psychiatric disorder may require formal psychiatric consultation.”
Finally, in April 1980 a consulting physician with the California Department of Rehabilitation noted Morgan’s complaints of chest pains and exertional weakness and commented that Morgan appeared “somewhat anxious.” Characterizing Morgan’s chest pains as likely psychogenic in origin, the physician described his prognosis as “poor.”
Morgan’s next medical contact of record occurred in December 1981. Dr. Mersch, consulting for the Secretary’s Disability Determination Services, examined Morgan and noted his numerous mental and physical difficulties. Morgan reiterated his complaint of chest pain. Morgan also complained of difficulties in thought and association, stated his hostility to the medical profession, and expressed his fear of pills. During the course of the exam, Morgan claimed to have died “at least 30 times” as a result of psychic surgery on his heart in Peru and Canada. Dr. Mersch diagnosed Morgan as suffering from, inter alia, “questionable nervous system defect and/or anxiety reaction” for which he recommended CAT scan and EEG evaluation for possible nervous system defect.
In late 1984, Morgan received his first recorded psychiatric assessment. Dr. Fried, a psychiatrist, commented in his report on the extent of Morgan’s decompen-sation and diagnosed him as suffering from psychosis, likely grounded in paranoid schizophrenia. Dr. Fried also recounted Morgan’s descriptions of his psychosurger-ies, special powers to fix mechanical objects, loss of reading ability because of “doping” by the medical profession, and penchant for carrying around a glass jar filled with broth which he claimed to be his lung tissue. He further characterized Morgan as currently incapacitated by somatic delusions, with poor prognosis for recovery without psychiatric care.
Taking into full account the course and progression of Morgan’s mental disability, particularly his obvious mental difficulties in the early months of 1980, one cannot help but conclude that his mental impairment approached disabling severity long before his actual diagnosis as schizophrenic in 1984. While Morgan admittedly re*1433ceived no psychiatric evaluation until 1984, he did receive care from other health care professionals — including an emergency room physician, a rheumatologist, and an occupational specialist — clearly documenting his deteriorating mental state in the critical months around December 1979. Accordingly, it was error for the Secretary to attempt to infer the onset date of Morgan’s disability without first appointing a medical advisor, or, alternatively, eliciting evidence from nonmedical sources if reasonable inferences about the progression of his impairment could not be medically established. See Lichter v. Bowen, 814 F.2d 430, 435-36 (7th Cir.1987) (ALJ erred in failing to appoint medical advisor according to terms of SSR 83-20 when onset date of claimant’s mental disability not subject to precise determination from administrative record); Naylor v. Sullivan, 1989 WL 58262, 1989 U.S.Dist. LEXIS 6080, 4 (N.D.Ill.1989) (same); Hadley v. Bowen, 1989 WL 18313, 1989 U.S.Dist. LEXIS 2084, 6 n. 3 (N.D.Ill.1989) (same); cf. Swanson, 763 F.2d at 1066 n. 2 (SSR 83-20 does not allow Secretary to rely on date of diagnosis as date of onset when “symptoms of disability and available medical evidence are consistent with a disability diagnosed only at a much later date”).
C.
The Secretary’s unexplained failure to apply SSR 83-20’s evidentiary guidelines underscores his broader error in failing to develop a full and complete administrative record on Morgan’s Title II disability claim. The courts have long recognized an AU’s special duty in social security cases to fully and fairly develop the record necessary to make an informed decision on a claimant’s entitlement to disability benefits. See, e.g., Dixon v. Heckler, 811 F.2d 506, 510 (10th Cir.1987) (disability hearing “a nonadver-sarial proceeding ” in which the AU has the basic duty of inquiry “to inform himself about facts relevant to his decision”) (emphasis added); Poulin v. Bowen, 817 F.2d 865, 870-71 (D.C.Cir.1987); Brown v. Heckler, 713 F.2d 441, 443 (9th Cir.1983). The ALJ’s responsibility to develop evidence takes on heightened significance when the claimant is mentally impaired. Deblois v. Secretary of Health & Human Services, 686 F.2d 76, 81 (1st Cir.1982); see also Poulin, 817 F.2d at 870-71. Failure to create an adequate administrative record constitutes good cause for remand under 42 U.S.C. § 405(g). See, e.g., Poulin, 817 F.2d at 870; Carrillo Marin v. Secretary of Health & Human Services, 758 F.2d 14, 17 (1st Cir.1985); Cannon v. Harris, 651 F.2d 513, 519 (7th Cir.1981) (per curiam).
At no point in the administrative proceedings related to Morgan’s Title II disability claim has an adequate record been developed on the question of when his mental condition became disabling. Morgan was the sole witness testifying at his disability hearing.4 Remarkably, the Secretary made no effort to ascertain from medical or lay witnesses Morgan’s mental condition during the critical time period around the December 1979 expiration date of his insured status. Because of this evidentiary gap, it is not possible to determine with any degree of certainty whether Morgan’s mental difficulties in 1984 represented the first active manifestation of his illness, or rather one of many instances of significant decom-pensation he had experienced over the last several years. This lack of record inquiry into the broad contours of Morgan’s mental illness, including its etiology, course, and severity, makes informed judgment impossible at this stage in the proceedings.
While mindful of the principle that the claimant carries the burden of proof on disability, the Secretary nonetheless retains the obligation to develop an adequate record necessary for intelligent appellate review. See Carrillo Marin, 758 F.2d at 17. I would thus reverse the judgment of the district court and remand to the Secre*1434tary for further proceedings designed to determine the period in which Morgan’s mental impairment reached disabling severity. See Mitchell v. Bowen, 827 F.2d 387, 389-90 (8th Cir.1987) (reversing and remanding Secretary’s denial of disability benefits for failure to fully develop record with respect to onset date of claimant’s disability); Poulin, 817 F.2d at 871-72 (remanding denial of schizophrenic claimant’s disability benefits for further development of evidence bearing on onset date of her mental disability); Deblois, 686 F.2d at 80-81 (same).
. The most common course of schizophrenia is one of acute exacerbations and relative remissions which rarely return the sufferer to baseline functioning. Textbook of Psychiatry at 767; DSM-III-R at 191. Moreover, while no pathognomonic clinical sign or symptom has yet been associated with schizophrenia, the illness invariably involves delusions, hallucinations, or certain characteristic disturbances in thought and affect in one or more of its phases. DSM-III-R at 187.
. Morgan’s complaints of somatic discomfort and feeling overwhelmed by internal and external pressures are signs consistent with the pro-dromal phase of schizophrenia. Textbook of Psychiatry at 759, 767; DSM-III-R at 190.
. Because the Crescent City clinic’s records are regularly destroyed after five years, no records exist as to the nature of Morgan’s treatment at the clinic during this period.
. Morgan's testimony at this April 1985 hearing provided scant assistance on the onset date issue as his mental impairment had progressed, by this time, to a level which prevented him from coherently responding to questions posed by the court and his counsel. Indeed, the ALJ characterized Morgan’s testimony as “bizarre and out of touch with reality."